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Page:Popular Science Monthly Volume 89.djvu/643

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Popular Science Monthly

��629

��Fig. 5. Fig. 6.

��The Aerial

The law.s permit amateur wireless stations to use any wavelcngtii up to 200 meters, provided tiiat the wave sent out is sharp and pure. This means that the aerial wire system to be used with t he sendinij appara- tus described must not be more than 7 5 ft.! o n p , measured along the conductor from its top to the ground connection. It is a good plan to use two wires about 50 ft. long running side by side to the top of a tree or chimney or special- ly built pole, keep- ing the wires about

five feet apart by fastening them at each end to a light wooden spreader. The top, and in fact the whole aerial, must be thoroughly insulated, if good results are to be secured. An excellent plan for preventing electrical leakage is to con- nect in series, with loops or rope, five or six porcelain insulators of the kind used in building the loading coil (Fig. 6). These are inserted between the spreader which carries the antenna wires and the rope halyard which is used to haul up the aerial. Similar strings of insulators must be used to guy out the bottom of the aerial. Where the lead-wireenters the house and con- nects to the instru- men ts it should pass through a thick porcelain tube, as shown in Fig. 7-

The ground connection may be made by wrapping several turns of bare copper wire tightly around a scraped water or steam-pipe. The connection should be made at a point near to the sending instru- ments.

���SPREADER

��Type of porcelain insulators The insulators connected in series

���LQftOING COIL

��SPARK GAP FI6.7

��Manner of connecting the several instruments making up the complete sending set

��If no water pipes are available, a large copper or iron plate may be buried deeply in moist cartii. As a rule, though, such earth connections are not as satisfactory as a pipe forming part of the town water system.

Connecting the Set

Theseveral instruments mak- ing up the complete sending set must be connected up as shown in Fig. 7. The spark-gap should be adjusted with its electrodes quite close together ■ — never more than y^ in. apart and at least half of the loading coil is to be put in series with the antenna. Unless a large part of this coil is used the trans- mitter will not radiate pure, sharp waves, and its use will violate the law and make its operator liable to prosecution by the government. If the spark-gap is kept short and a considerable portion of the loading coil used, there will be nothing to fear so long as neither of the aerial wires is over 75 ft. in length.

Whenever the key is pressed, if the set is properly connected and ad- justed, a bright, snappy, singing spark will jump across the gap. Each spark starts a train of high fre- quency currents oscillating back and forth in the aerial wires, and a train of electromagnetic waves is radiated into space. A suit- able wireless receiver located where a (jortion of these radiated waves will reach it, will pick up some of their energy and produce from it a sound which, indicates the dot-and-dash buzzes of a Morse signal.

( To he continued)

��GROUND

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